U.S. Pat. No. 4,361,681 teaches that polyester containing anhydride end-cap agents have a reduced acetaldehyde generation rate.
U.S. Pat. No. 5,459,224 discloses polyesters having 4-oxybenzylidene end-cap agents to impart improved weatherability and photostability, but no mention is made as to evolution of acetaldehyde. However, it is indicated that such polyesters are suitable for food and beverage packaging.
Polyesters can be synthesized by a number of routes known in the art using a variety of catalyst systems. EP 826,713 A1 teaches that lower levels of acetaldehyde occur during copolymerization of PET when a phosphite such as bis(2,4-di-tert-butylphenyl)-pentaerythritol phosphite is present during the polymerization.
U.S. Pat. Nos. 4,837,115; 5,258,233; 5,266,413; 5,340,884; 5,648,032 and 5,650,469; and WO 93/20147 A1; WO 93/23474 A1; WO 98/07786 and WO 98/39388 teach the use of polyamides as a means of reducing the concentration of acetaldehyde, presumedly via a Schiff-base reaction with the aldehyde, which is reversible in the presence of water.
U.S. Pat. No. 5,856,385 teaches the use of polyamide or amide-wax to reduce the level of acetaldehyde which occurs when sorbitol-based clarifying agent is heated in polyolefins.
U.S. Pat. No. 5,011,890 describes the suppresion of formaldehyde formation when polyacrylamide, polymethacrylamide or selected acrylamide or methacrylamide copolymers are used in polyacetals. A requirement is that the polyacrylamide or polymethacrylamide must be “non-meltable” at the processing temperature of polyacetal. There is no suggestion in this patent that using polyacrylamide or polymethacrylamide in a polyester would reduce the concentration of acetaldehyde in a melt-mixed blend such as via extrusion.
The invention is useful for any polyester where aldehydic compounds, especially acetaldehyde, are formed or evolved during thermal processing of said polyester. Thermal processing of PET includes the synthesis of PET, thermal exposure during solid state polymerization (SSP), any injection molding, injection-blow molding or stretch-blow molding used in the manufacture of preforms, parissons or bottles and containers, or extrusion of film, or during any melt processing of PET above its glass transition temperature and below its decomposition temperature.
The instant invention provides for a lower amount of contaminants (e.g. aldehydes) in PET water bottles thus providing for improved taste or flavor in bottled water or other bottled beverages in said PET containers. The reduction in the amount of acetaldehyde is highly beneficial in this respect. Acetaldehyde is known as a decomposition product of polyesters such as PET. The acetaldehyde imparts an undesirable taste or flavor to bottled water stored in PET bottles. It has been a long sought objective of the industry to reduce the level of acetaldehyde which migrates out of the PET bottle walls into the water or other beverage stored therein. A number of engineering or design changes to extruders, injection molding machines for preforms and bottle making machinery have been made to minimize formation of acetaldehyde when poly(ethylene terephthalate) PET is processed Modification to the PET composition itself have been made to lower its melting point or its melt viscosity in order to allow less severe thermal or mechanical damage when PET is processed into preforms or bottles.